This application is based on an application No. 11-29308 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention pertains to a solid scanning optical writing device to write images using a PLZT light shutter array or LED array, light amount correction method therefor and light amount measuring device.
2. Description of the Related Art
Various optical writing devices have conventionally been provided that form images on photographic paper or film using a silver halide material, or on an electrophotographic photoreceptor, by controlling the light for each pixel using a light shutter array or LED array comprising PLZT or other elements. In such an optical writing device, line noise may occur in the output image due to a variation in the amount of light passing through or emitted from the optical elements of the light shutter array or LED array. In order to eliminate this noise, the light amount output from each optical element is measured, correction calculation is performed based on the measurement results, and correction of the light amount variation (shading correction) is performed.
In measuring the light amount, it is preferable from the standpoint of ensuring measurement accuracy and making the measuring device small in size that the light amount from each optical element of the light shutter array, etc., be directly measured. However, it is not easy to accurately measure the light amount from each of the optical elements, which have an extremely dense arrangement in order to form high resolution images, and correlate the measurement results to each optical element.
FIGS. 8 and 9 show how light amount measurement is conventionally performed. They show how the amount of light that passes through each light shutter 31 (optical element) of the PLZT light shutter array is measured by means of a measuring device. The multiple light shutters 31 are aligned in two lines. A light shutter 31 of one line is located between two light shutters 31 of the other line. When voltage is impressed, the light shutter 31 causes the plane of polarization of the light that entered it from behind to rotate, allows the light to pass through and outputs it from the front. When voltage is not impressed, the plane of polarization of the light that enters the light shutter 31 from behind does not rotate and the light is output from the front just as it struck the light shutter. 91 indicates a light receiving mask located in front of the sensor that receives the light from the light shutters 31. In FIG. 8, the light receiving mask 91 has a slit 91a with the same configuration as the light shutter 31, and regulates the light that strikes the sensor. The light receiving mask 92 shown in FIG. 9 has a slit 92a, the length of which that runs along the secondary scanning direction perpendicular to the length of the lines of the light shutter is equal to the length of the light shutter 31. When the amount of light passing through the light shutter 31 is measured using such a mask 91 or 92, the light amount output from each light shutter 31 may be accurately measured.
However, when a light shutter array is actually used as an optical writing device, from the standpoint of efficiency of use of the light, and to ensure that the necessary distance from the exposure surface is maintained, an image forming lens (selfoc lens array) is often used together with the light shutter array. FIG. 10 is a view of the positional relationship between a selfoc lens array and the light shutters 31 of a PLZT light shutter array. Ordinarily, due to the effect of the selfoc lens array on the image forming resolution (hereinafter xe2x80x98MTFxe2x80x99), the output light from the light shutters 31 is slightly blurred when it forms an image on the exposure surface.
Because a selfoc lens array comprises multiple rod lenses 35a aligned in a zigzag fashion, as shown in FIG. 10, the MTF varies depending on the positional relationship between the light shutters 31 and the rod lenses 35a. In other words, the image formed on the exposure surface by the output light from the light shutters 31 may be sharp or blurry depending on the area. Where light is output from both lines of the light shutters 31, the light amount from the gap between light shutters 31 (trough light amount) does not become completely zero. As explained above, where the light shutters 31 are aligned in a zigzag fashion such that they form two lines, exposure is performed by means of the light from a particular light shutter 31, to which some of the light from the neighboring light shutters 31 located in the other line is added.
In addition, in the manufacturing process by which the light shutters 31 are aligned in a zigzag fashion such that they form two lines, a groove 32 (see FIGS. 8 and 9) is formed between any two light shutters 31, and a slight amount of light escapes of this groove 32. This escaping light affects the actual exposure as well.
Due to the details explained above, correcting the variation in light amount among the optical elements simply based on the information on the light amount measured using the mask 91 or 92 shown in FIG. 8 or 9 is insufficient to correct the variation in light amount on the exposure surface where an image is actually formed, and a variation in light amount still occurs on the exposure surface.
The object of the present invention is to provide an improved solid scanning optical writing device, light amount correction method therefor and light amount measuring device.
Another object of the present invention is to provide a solid scanning optical writing device, light amount correction method therefor and light amount measuring device that are capable of accurately measuring the output light amount of each optical element and performing good light amount correction.
Yet another object of the present invention is to provide a solid scanning optical writing device, light amount correction method therefor and light amount measuring device in which the variation in light amount among the optical elements is corrected on the exposure surface where an image is formed.
In order to attain these and other objects, one aspect of the present invention comprises a solid scanning optical writing device that, based on the image data, turns ON/OFF the multiple optical elements that are aligned in a zigzag fashion such that they form two lines in the main scanning directions, said optical writing device having a light amount measuring unit including a light amount sensor to measure the amount of light output from the optical elements, wherein the light receiving area of the light amount sensor has an open slit and the length of the opening of the slit in the secondary scanning direction is set to be as long as or longer than the length of the optical element in the secondary scanning direction.
Another aspect of the present invention comprises a light amount measuring device having a light amount measuring unit including a light amount sensor to measure the amount of light output from the multiple optical elements aligned in a zigzag fashion such that they form two lines, a means to move the light amount measuring unit forward and backward in the direction of the alignment of the optical elements, and a means to adjust the position of the light amount measuring unit, wherein the light receiving area of the light amount sensor of the light amount measuring unit has an open slit and the length of the opening of the slit in the direction perpendicular to the direction of the alignment of the optical elements is set to be as long as or longer than the length of the optical element.
Yet another aspect of the present invention comprises a light amount correction method for the solid scanning optical writing device, wherein this method turns ON/OFF the multiple optical elements aligned in a zigzag fashion such that they form two lines in the main scanning directions based on the image data, and has (i) a process in which only the optical elements in one of the two lines are caused to illuminate and the amount of light output from the optical elements of this line is measured while the light amount measuring unit is caused to be moving in the main scanning directions, (ii) a process in which only the optical elements in the other line are caused to illuminate and the amount of light output from the optical elements of this line is measured while the light amount measuring unit is caused to be moving in the main scanning directions, and (iii) a process in which the correction amount regarding the amount of light output from each optical element is calculated from the ridge light amount of the optical element and the trough light amount from the space located at the same position as the optical element but in the other line.
Using the construction described above, because not only the ridge light amount (the maximum light amount) of the optical element but also the trough light amount (the light amount from between two optical elements) of the space located at the same position as the optical element but in the other line is added into the calculation, the amount of light output from each optical element may be measured with accuracy, making it possible to obtain highly accurate shading correction (light amount variation correction).
In addition, by making the length of the opening of the slit of the light amount sensor light receiving area in the secondary scanning direction sufficient to cover the two lines of optical elements aligned in a zigzag fashion, the amount of light escaping from the groove between any two optical elements may be detected, making the light amount correction more accurate.
Further, in the process in which the amount of correction of the optical element output light amount is calculated, by calculating the optical resolution per unit length from the alignment pitch of the optical elements and calculating the amount of correction regarding the optical element output light amount using this optical resolution, the trough light amount (the light amount from between two optical elements) when the ridge amount (the maximum light amount) for the optical element changes is calculated, making better light amount correction possible.